Power transmission



April 1 c. BENNETT ET'AL 2,790,135

POWER TRANSMISSION Filed Dec. 8, 1955 Shoots-Sheet 1 PRIOR ART CONTROL SIGNAL SOURCE BIAS SOURCE FIG. I

WITH K COMPENSATING CIRCUIT (FIG.2)

WITHOUT COMPENSATING CIRCUITIFIGJ) CURRENT OUTPUT CONTROL CURRENT [Wm/mks.

CLARENCE BENNETT LEISTER w. BUECHLER ATTORNEY April 23, 1957 Filed Dec. 8. 1955 c. BENNETT ET L 2,790,135

POWER TRANSMISSION 2 Sheets$heat 2 a 34 2 T .5. F L. 20 5e 4g I I v 7' I 38 so 36 v 30 l A A l f I I I I I l A A A I F W 24 I v K --s4 I I I I )EEEH v CONTROL 52 |6 1 l8 H 2 I 50 SIGNAL SOURCE INVENTORS CLARENCE BENNETT LESTE R W. BUECHLER ATTORNEY United States Patent POWER TRANSMISSION Clarence Bennett, Lemay, and Lester W. Buechler, Kirkwood, Mo., assignors to Vickers, Incorporated, Detroit, Mich., a corporation of Michigan Application December 8, 1955, Serial No. 551,904

15 Claims. (Cl. 323-89) This invention relates to power transmission and more particularly to magnetic amplifiers.

One of the many types of magnetic amplifiers is the self-saturating bridge. Such amplifiers have a pair of adjacent saturable reactor branches connected at one end to a common A. C. terminal, the other ends of the branches being connected across the load diagonal 'of the bridge. Each of the branches include a one-way valve connected in series with the impedance or power winding of a saturable reactor to provide self-saturation in the well-known manner. The one-way valves are oppositely related to conduct on alternate haif cycles of an applied A. C. voltage.

Multiphase bridge type self-saturating magnetic amplifiers are subject to the following problem and condition which does not occur in single phase bridge type self-saturating magnetic amplifiers. In any conventional multiphase bridge type self-saturating magnetic amplifier, the rates of flux change and consequently the voltages across the reactors in adjacent reactor branches are considerably unbalanced, the unbalance being due in most part to the fact that each reactor is affected not only by the principal conduction current of its own branch, but also because it cyclically sees the voltage of the load due to the principle conduction currents of the other branches. Thus, at any instant the voltages across the reactors in adjacent reactor branches are necessarily unbalanced and too far from the desirable 180 phase relation, resulting in an output loss which in some threephase amplifiers reaches 20% or more.

Although the exact reason for this loss is not known for certain, it is believed that cyclic unbalance between the reactors in each pair of adjacent reactor branches produces a spinning neutral under which conditions the voltages between the vertices and the floating neutral of the voltage vector diagram of the polyphase bridge amplifier are considerably less than they would be if the neutral were symmetrically fixed, thus reducing the total output.

The reactors in adjacent reactor branches of a polyphase bridge can be locked in balanced phase opposition by connecting a resistor or a capacitor across the pair of reactors in adjacent branches to allow an even harmonic balancing current to flow. However, both expedients have serious side effects. Capacitors large enough to be efifective, in many cases, cause resonance problems such as periodic oscillations, tripping action, and hunting. Resistors shorted across the reactor pairs introduce unwanted changes in the response time of the amplifier, and also introduce negative feedback. If the latter situation is remedied by inductively coupling the resistor across the two reactor power windings the time constant problem remains, and if the resistor is connected across the control winding an undesirable signal drain is introduced.

In accordance with the present invention the output of a polyphase bridge type self-saturating magnetic amplifier is substantially improved, without serious side effects, by means of a compensating loop circuit which 2,790,135 Patented Apr. 23, 1957 includes an asymmetric device and is coupled to the reactors of adjacent reactor branches to subject the loop circuit to the differential of the instantaneous flux and voltage conditions of the reactors, the current conduction through the device being in a direction to generate mmfs. in the reactors in aiding relation to the self-saturating fiux. The current forced through the loop circuit by the ditferential voltages across the reactor power windings, due to the tendency of the flux in the inactive reactor to decay at a more rapid rate than the flux buildup in the active reactor, opposes the more rapid flux decay tendency in the inactive reactor thus substantially equalizing the rates of the flux channges in the two reactors thereby to substantially balance the voltages thereacross and lock the reactors in proper phase for greater output.

It is therefore an object of the present invention to provide a new and useful magnetic amplifier circuit.

Another object of the present invention is to provide means for increasing the output of a poly hase bridge type self-saturating magnetic amplifier.

Another object of the present invention is to improve a polyphase bridge type self-saturating magnetic amplifier by balancing the reactors in adjacent reactor branches with circulating current forced through an asymmetric circuit loop which includes, in series opposition, the power windings of the two reactors.

Another object of the present invention is to provide means for increasing the gain of a polyphase bridge type self-saturating magnetic amplifier.

A further object of the invention is to improve a polyphase bridge type self-saturating magnetic amplifier by means of a loop path which includes a unidirectional device and the two reactor power windings of adjacent reactor branches in series opposition.

Further objects and advantages of the present invention will be apparent from the following description, reference .being had to the accompanying drawings wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a schematic diagram of a conventional three phase bridge type magnetic amplifier well known in the prior art;

Fig. 2 is a schematic diagram of a polyphase bridge type magnetic amplifier embodying features of the present invention, and

Fig. 3 is a chart with comparative output curves showing improvement in output gained by the present invention.

Referring now to Fig. 1 which shows a polyphase bridge magnetic amplifier of the prior art, each power input terminal is connected to a pair of self-saturating reactor branches whose other ends are connected across the load diagonal of the bridge. Each reactor branch being a conventional half-wave self-saturating reactor circuit, includes the usual one-way valve connected in series with the power winding of a saturable reactor. The saturable reactors are provided with control windings which may be energized with an adjustable control signal, thereby to adjust the output of the amplifier.

According to the present invention, a bridge type selfsaturating magnetic amplifier circuit such as the type in Fig. 1 is considerably improved in the manner shown in Fig. 2, which shows the basic circuit of Fig. 1 modified by the addition of an asymmetric compensating circuit which extends the output range of the amplifier.

In Fig. 2 a three-phase bridge type self-saturating magnetic amplifier has three pairs 10, 12, and 14 of adjacent bridge branches. The branches in each pair are commonly connected together at one end to an A. C. input terminal of the bridge, the other ends of the branches being connected across the output terminals 16 and 18' of the bridge. For example, the pair of adjacent branches is connected at one end to an A. C. input terminal 20. The adjacent branches in the pair 12 are connected to an A. C. input terminal 22, and the pair 14 of adjacent branches are connected to an A. C. input terminal 24. The input terminals 20, 22 and 24 constitute the power input diagonals of the bridge when taken in the following association: and 22 forming one diagonal, 22 and 24 a second diagonal, and 20 and 24 a third diagonal. The output terminals 16 and 18 constitute the load diagonal of the bridge. Input terminals 20, 22 and 24 are connected to a source 26 of three phase alternating current.

Each of the pairs of adjacent branches being similar, only one pair, for example pair 10, need be described. Pair 10 includes the adjacent branches 28 and 30, each of which has connected therein a one-way valve in series with the power winding of a saturable reactor. In branch 28 the one-way valve is at 32 and the reactor power winding is at 34, while in the branch 30 the one-way valve and the winding are indicated at 36 and 38, respectively. With respect to the applied supply voltage or to any common point in the circuit, for example terminal 20, the valves 32 and 36 are oppositely poled, that is, they are reversely related to each other. One-way valves of any suitable type may be employed, for example metallic rectificrs such as selenium cells. For convenience valves 32 and 36 will hereinafter be referred to as the power valves.

Although the windings 34 and 38 may be carried on separate magnetic cores, they are shown in the illustrated embodiment as being wound on the respective outer legs of a three-legged saturable magnetic core 40, which also carries on its center leg a bias winding 42 and a control winding 43. Preferred core materials for magnetic amplifiers have narrow, substatnially rectangular, dynamic hysteresis loops. Although the reactor power windings of both branches are shown on a single three-legged core and employ a comomn control and a common bias winding, it is Well known that this arrangement is in effect two distant reactors, one associated with one branch and including one power winding and one half of the core, while the other reactor is in the other branch and includes the other half or": the core and the second power winding. Thus, the reactor in branch 28 may be generally indicated at 44 while the reactor in branch 30 may be indicated at 45.

Bias current may be supplied to the bias windings of all the reactors in the respective pairs from any suitable source, for example, a rectifier 46 whose input is connected across one of the phases of the A. C. supply source 26 and whose output is connected through an adjustable impedance 4% to all of the bias windings. All of the control windings 43 of the reactors in the respective pairs are connected to a source of control signals 50 through an adjustable impedance 52. The signal source 50 may be unidirectional current from a battery, a generator, a detector, the output of another amplifier, or any other suitable source. As is well known, with the control coils properly oriented and the control signal properly phased, the control signal may be alternating currentfrom any suitable source. Likewise, the current to the bias windings 42 may also be properly phased alternating current.

The circuit thus far described is conventional and its operation is well known and will not be gone into with great detail. Considering the operation of one particular pair of branches, for example pair It) (branches 28 and 30), the operation is as follows. During one half cycle of the applied supply voltage from the source 26, for instance the half cycle during which valve 32 is conduc tive and valve 36 is nonconductive, current will flow from the alternating current supply source 26 through the reactorwinding 34, valve 32, the load, and back to the source 26 through one or both of the other phase conductors depending on the portion of the half cycle being considered. On the opposite half cycle, the valve 36 is conductive and current will flow from one or both of the other phase conductors through the load in the same direction and then through valve 36 and reactor power winding 38 back to the source 26. The load current flow depends on the impedance of the reactors which in turn is dependent upon the premagnetization or the degree of magnetic saturation of the reactor cores. The degree of magnetization of the core of a particular reactor during the nonconductive period of its associated power valve controls the firing angle of the reactor section involved. During this critical period the core saturation may be decreased or increased as desired by adjusting the amplitude or sense, or both, of the control current supplied to the control coil 43. The direction of current through any winding which produces mmfs. tending to drive the amplifier up, that is rnmfs. in aiding relation to the fluxes of self-saturation, shall be referred to as the saturating direction and any mmfs. produced by such current shall be referred to as saturating rntnfs.

For a given set of parameters the circuit thus far described will have a particular control characteristic for a given supply voltage, for example, the control characteristic represented by Curve A in the chart of Fig. 3 wherein the X axis represents control current and the Y axis output current. For the same set of given parameters and conditions the output of the amplifier is increased, for example to the position represented by the upper end of the dashed Curve B, by adding, in accordance with the present invention, to the circuit thus far described, similar compensating circuits 54 in each of the pairs 10, 12 and 14 of adjacent reactor branches. Each compensating circuit is a series loop including, in series opposition, the reactor power windings of adjacent reactor branches and an asymmetric link poled to pass current mainly in the saturating direction.

Again considering the pair 10 of adjacent arms for explanatory purposes, it will be seen that compensating circuit 54 is a series loop including power windings 34 and 38 in series opposition with respect to fundamental frequency voltages and an asymmetric link 56 connected to the respective junctions 58 and 60 between the power winding and power valve of each of the branches 28 and 30. Asymmetric link 56 may be, for example, a one-way valve such as a metallic rectifier, for example a selenium cell.

It will be noted that like electrodes of the valves 32 and 56 are connected together at the junction 58 and that like electrodes of the valves 36 and 56 are tied to the junction 60. Thus, with respect to each power winding, its associated power valve and the valve 56 are similarly poled or related, and therefore the current flow around the loop circuit including the power windings and the valve 56 will be in the same direction through each power winding as the current flow through the winding and its associated power valve when that valve is conducting. Under these conditions the mmfs. produced in the reactor core sections by the circulating current in the compensating loop circuit 54 is in the same direction as the mmfs. produced in the cores by the load current flowing in the forward direction of each power valve during its conductive or active half cycle. To state it briefly, the valve 56 is poled to pass current through the compensating circuit in the saturating direction. It will be noted that the power valves 32 and 36 together with the load are bypassed by the compensating loop circuit 54 and excluded therefrom.

As hereinbefore stated the rates of flux change and consequently the voltages of the respective reactor sections of the adjacent reactor branches 28 and 30, are more nearly balanced in opposite phase by the circulating current forced through the compensating loop 54 by the voltage differential between the reactor sections associated with the respectivewindings 34 and 38. By the expres' sion balanced in opposite phase is meant that 'at -any instant the fundamental voltages across the two reactor windings 34 and 38 are equal and opposed with respect to the common connection of the windings at the input terminal 20 and across the points 58 and 60. The instantaneous sign of these voltages is the same for both windings at the common terminal 20 and is also the same for both at points 58 and 60. Thus, if the fundamental voltages across the power windings were exactly equal and symmetrical there would be no fundamental voltage across points 58 and 60. Fundamental frequency quantities in the reactors of adjacent branches are in opposition tending to free the compensating circuit of fundamental frequency currents. For example, the windings 34 and 38 being included in series opposition in the compensating circuit 54, the fundamental frequency voltage across winding 34 is in opposition to the fundamental frequency voltage across winding 38, making the compensating circuit 54 substantially free of fundamental frequency current. While the fundamental flux produced by the load current is building up in the reactor of one adjacent branch it is decaying in the reactor of the other branch of a pair of adjacent branches, and the compensating circuit is always subjected simultaneously to the flux decay of one reactor and to the flux build-up in the other reactor. The net result is that the compensating circuit 54 is always subjected to the differential of the instantaneous flux conditions of both reactors. It was found that, in actually tested polyphase circuits, the compensating circuits 54 effected as much as 20% and more increase in the amplifier output.

Even if only one pair of adjacent reactor branches in a polyphase bridge magnetic amplifier is equipped.

with the compensating circuit the amplifier is impoved by an increase of the output. For example, if the pair 10 of adjacent branches has a compensating loop circuit 54, and the other pairs 12 and 14 do not have the compensating circuits, there is still some advantage gained and an increase of total amplifier output.

If some negative feedback is desired the valve 56 may be chosen with high leakage or a resistor may be shunted across the valve 56, the compensating loop circuit however still remaining an asymmetric circuit.

The arrows under the respective power windings show the relative mmf. directions of those windings during the conductive or active periods of the respective power valves associated therewith. The arrows under the other windings indicate the mmfs. produced by those windings. For example, the mmfs. of the bias windings oppose those of the control and of the power windings, thus indicating negative bias.

It will be apparent from the curves of Fig. 3 that the compensating circuit 54 increases both the output and the gain of polyphase bridge type self-saturating magnetic amplifier.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A three-phase bridge type self-saturating magnetic amplifier comprising a power input circuit, an output circuit, and a plurality of pairs of adjacent bridge branches, each branch including a saturable reactor element with a power winding and a one-way valve connected in series with the winding for self-saturation, the valves in each pair being reversely related, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, each pair of adjacent bridge branches having an asymmetric loop circuit exclusively for that pair and including in opposed relation the reactor power windings of that pair of adjacent branches and excluding the valves of that pair of branches, said loop circuit being poled to permit current flow there. through mainly in the saturating direction.

2. A polyphase bridge type self-saturating magnetic amplifier comprising a power input circuit, an output circuit, and a plurality of pairs of adjacent bridge branches, each branch including a saturable reactor connected with a one-way valve for self-saturation, the valves in each pair being reversely related, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, each pair of adjacent bridge branches having means for circulating current in said reactors of that pair of branches in response to the resultant voltage relations of those reactors, said means comprising a series loop circuit including a unidirectional device and in opposed relation said reactors of that pair of branches and excluding said valves of that pair of branches, said device being poled to pass current through said loop circuit in the saturating direction.

3. A three-phase bridge type self-saturating magnetic amplifier comprising a power input circuit, an output circuit, and a plurality of pairs of adjacent bridge branches, each branch including a saturable reactor and a oneway valve connected for self-saturation, the valves in each pair being reversely related, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, and each pair of adjacent branches having a unidirectional loop circuit exclusive to that pair and including in series opposition said reactors of that pair of adjacent branches but excluding said valves, said loop circluit being poled to allow current flow therethrough in the saturating direction.

4. A polyphase bridge type self-saturating magnetic amplifier comprising a power input circuit, an ouput circuit, and a plurality of pairs of adjacent bridge branches, each branch including a one-way valve and a saturable reactor having core means and a power winding carried by the core means and connected to the one-way valve for self-saturation, the valves in each pair being oppositely poled, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, and each .pair of adjacent branches having an asymmetric loop circuit independent of the other branches and including Winding means inductively related to said core means of that pair of adjacent branches but excluding said valves, the reactors of that pair of branches being arranged so that fundamental frequency quantities of both are oppositely related to each other with respect to said winding means in the loop circuit of that pair of adjacent branches whereby said loop circuit is substantially free of fundamental frequency current, said loop circuit being poled to allow current flow therethrough mainly in the saturating direction.

5. A polyphase bridge type self-saturating magnetic amplifier comprising a power input circuit, an output circuit, and a plurality of pairs of adjacent bridge branches, each branch including a saturable reactor and a one-Way valve connected for self-saturation, the valves in each pair being oppositely poled, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, and each pair of adjacent branches having a series loop circuit independent of the other branches and including a unidirectional device and the reactors of that pair of adjacent branches but excluding the valves of that pair of branches, means placing fundamental frequency quantities in said reactors in opposition whereby said loop circuit is substantially free of fundamental frequency current, said device being poled to pass current through the loop circuit in the saturating direction.

6. A polyphase bridge type self-saturating magnetic amplifier comprising a power input circuit, an output circuit, and a plurality of pairs of adjacent bridge branches,

area-tea each branch including saturable reactor means with core means carrying a power winding and a one-way valve connected to the power winding for self-saturation, the valves in each pair being oppositely poled, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, each pair of adjacent bridge branches having an asymmetric loop circuit independent of the other branches and including winding means inductively related to the core means of that pair of adjacent branches, said loop circuit excluding said valves, and said loop circuit being poled to permit current flow therethrough mainly in the saturating direction.

7. A three-phase bridge type self-saturating magnetic amplifier comprising a power input circuit, an output circuit, a plurality of pairs of adjacent bridge branches, each branch including a saturable reactor power winding and a one-way valve connected in series with the winding, the valves in each pair being reversely related, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, and an asymmetric loop circuit including in series opposition said power windings of a pair of adjacent branches but excluding said valves of that pair of branches, said asymmetric loop circuit being poled to permit current flow therethrough mainly in the saturating direction.

8. A polyphase bridge type self-saturating magnetic amplifier comprising a power input circuit, an output circuit, and a plurality of pairs of adjacent bridge branches, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, each branch including a saturable reactor power winding and a one-way valve connected in series with the winding, each branch having a circuit point between the winding and the valve or the branch, the valves in each pair being reversely related, the valve end of the branches being connected to the output circuit, each pair of adjacent branches having a loop circuit including said windings of that pair of branches and an asymmetric link connecting said points of: that pair of branches, said asymmetric link being poled to permit current flow through the loop circuit mainly in the saturating direction.

9. In a polyphaso bridge type self-saturating magnetic amplifier having a plurality of power input terminals, an output circuit and a plurality of pairs of adjacent bridge branches, each branch including a saturable reactor power winding connected in series with a one way valve, one end of the branches in each pair being connected'together to one of said terminals, the other end of said branches of each pair being connected across said output circuit, the combination therewith of a series loop circuit COID- prising said power windings of a pair of adjacent branches and a one-way valve coupled across said windings, said last valve being poled to pass circulating current through said loop circuit in the saturating direction.

ii). In a polyphase bridge type self-saturating magnetic amplifier having a plurality of power input terminals, an output circuit and a plurality of pairs of adjacent bridge branches, each branch including a. saturable reactor power winding connected in series with a one-way valve, each branch having circuit point between the windir the valve, the valves in each pair of branchebein versely related, one end of the branches in ach pair ban connected togetl'rer to one of: said terminals, the other end of said branches of each pair being connected acnass said output circuit, the valve ends of the branches of at least one of said pairs of adjacent bridge branches being connected to the output circuit, the combination there with of a unidirectional device connected between said points of said one pair of adjacent bridge branches, said device being poled to circulating current through said windings of said one pair of adjacent branches in the saturating direction.

till

11. Ina polyphase bridge type self-saturating magnetic across said output circuit, the combination therewith of a loop circuit inductively related to said reactors of a pair of adjacent bridge branches and including in series a unidirectional device, said device being poled to pass circulating current through said loop circuit in the saturating direction, and means for opposing fundamental frequency quantities in said reactors related to said loop circuit whereby said'loop circuit is substantially free of fundamental frequency currents.

12. In a polyphase bridge type self-saturating magentic amplifier having a plurality of power input terminals, an output circuit and a plurality of pairs of adjacent bridge branches, each branch including saturable reactor means connected with a one-way valve for self-saturation, the valves in each pair of branches being oppoistely related, one end of the branches in each pair beingconnected together to one of said terminals, the other end of said branches of each pair being connected across said output circuit, the combination therewith of a series loop circuit comprising a unidirectional device and said reactor means of a pair of adjacent bridge branches and excluding said valves of those branches, said device being poled to passcirculating current through said loop circuit in the saturating direction.

13. In a polyphase bridge type self-saturating magnetic amplifier having a plurality of power input terminals, an output circuit and a plurality of pairs of adjacent bridge branches, each branch including a saturable reactor power winding connected in series with a oneway valve, the valves in each pair of branches being reversely related, one end of the branches in each pair being connected together to one of said terminals, the other end of said branches of each pair being connected across said output circuit, the combination therewith of a series loop circuit comprising a unidirectional device and in series opposition said power windings of a pair of adjacent bridge branches, said valves of that pair of branches being excluded from the loop circuit, said device being poled to pass circulating current through said loop circuit in the saturating direction.

14. In a polyphase bridge type self-saturating magnetic amplifier having a power input circuit, an output circuit, and a plurality of pairs of adjacent bridge branches, each branch including a saturable reactor with a power winding and a one-way valve connected in series with the wind-.

ing, the valves in each pair being reversely related, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, the combination therewith of an asymmetric loop circuit inductively coupled to said reactors of a pair of adjacent bridge branches, said loop circuit being responsive to the differential of the flux decay of one reactor in that pair and the flux buildup of the other reactor in that pair, said loop circuit being poled to permit current flow therethrough mainly in the saturating direction.

15. A three-phase bridge type self-saturating magnetic amplifier comprising a power input circuit, an output circuit, and a plurality of pairs of adjacent bridge branches, one end of both branches in each pair being coupled to the input circuit, the other ends of the branches in each pair being connected across said output circuit, each branch including a saturable reactor power winding and a one-way valve connected in series with the winding, each branch having a circuit point between the winding and the valve of the branch, the valves in each pair being 10 reversely related, the valve end of the branches being conbranches, said asymmetric link being poled to permit curnected to the output circuit, each pair of adjacent rent flow through the loop circuit mainly in the saturating branches having a loop exclusively for that pair and indirection.

eluding said winding of that pair of branches and an asymmetric link connecting said points of that pair of 5 N0 references cited- 

